1. Field of the Invention
This invention relates to a magnetic disc drive motor, and particularly relates to a rotating support device for rotatably supporting a magnetic disc.
2. Related Art
The examples of conventional magnetic disc motors built into hard disc drive devices are shown in FIGS. 4 and 5. In the magnetic disc drive motor shown in FIG. 4, a shaft 2 is mounted in a frame 1, and two ball bearings 3, 3 are mounted on the shaft 2. A hub 4 is mounted on the ball bearings 3, 3. The central portion of the hub 4 is cylindrical-shaped, and this cylindrical central portion is open at its upper and lower ends. Two magnetic discs 5 are mounted on the outer peripheral surface of the cylindrical central portion. A seal cover 6 covers the opening at the upper end of the hub 4 and is fixed in position there by an adhesive 7.
An armature core 8 is secured on the frame 1, and a drive magnet 9 is mounted on the inner surface of the cylindrical peripheral portion of the hub 4. The armature core 8 has a number of salient poles, and a coil 10 is wound around each of the salient poles. The outer surface of the armature core 8 faces the inner surface of the drive magnet 9 across a radial gap. When the armature core 8 is excited with an electric current it causes the drive magnet 9 to rotate, and the hub 4 rotates integrally with the drive magnet 9.
In the magnetic disc drive motor shown in FIG. 5, in order to make the device smaller and thinner, the motor is housed directly inside the hub on which the magnetic discs are loaded. A cylindrical support 12 is formed in the central part of a frame 11, and two ball bearings 13, 13 are mounted on the inner surface of this support 12. A shaft portion 15, integral with the hub 14, is rotatably mounted in the bearings 13, 13. The magnetic discs 5 are mounted on the outside of the hub 14.
An armature core 16 is mounted on the outer surface of the support 12 of the frame 11, a drive magnet 17 is fixed on the inner surface of the hub 14, the armature core 16 and the drive magnet 17 and other parts form a motor, this motor rotates the drive magnet 17 so as to rotate the hub 14 together with the drive magnet 17.
In the conventional magnetic disc drive motors described above, because they incorporate the hub 4 for mounting the magnetic discs 5, the precision of coupling the hub 4 with the ball bearings 3 and the precision of machining the hub 4 directly affect the precision with which the magnetic discs 5 rotate, and the precision with which the magnetic discs 5 rotate is therefore impaired. Also, because the diametral thickness of the hub 4 has to be accommodated, there is the problem that it is difficult to reduce the size of the motor, and, in particular, when high density magnetic discs 5 which are both of small diameter and capable of high density recording are used, because the diameters of the shaft 2 and the ball bearings 3 have to be made small, problems such as shaft deflection occur, and the practical application of these high performance discs is difficult.